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BY JUSTIN RAY
Follow the countdown and launch of the Delta 4-Heavy rocket with classified payload for the U.S. National Reconnaissance Office. Reload this page for the very latest on the mission.
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Heading eastward on 1.9 million pounds of ground-shaking thrust, the rocket put on quite a display with its 200-foot-long fiery plumes from the three main engines

The giant vehicle is created by taking three Common Booster Cores -- the liquid hydrogen-fueled motor that forms a Delta 4-Medium's first stage -- and strapping them together to form a triple-body rocket, and then adding an upper stage.

Shortly after the upper stage ignited and the 65-foot long nose cone peeled away, the flow of official information about the launch ceased because of the clandestine payload riding atop the rocket.

The Air Force had said in the past that this launch, which is known as the NROL-26 mission, would be another three-burn ascent profile and follow a launch timeline similar to the one demonstrated during the 2004 test flight of the Delta 4-Heavy. That meant the upper stage would perform its first two maneuvers in quick succession, then take a long orbital coast before delivering a final boost and releasing the payload several hours after liftoff.

It is presumed that the rocket flew directly into geosynchronous orbit 22,300 miles above the planet to deploy the classified spacecraft for the U.S. National Reconnaissance Office, the secretive government agency that designs and operates the country's spy satellites.

The NRO doesn't disclose the identities of the satellites it is launching or what the craft will do, so there's no official information about the craft carried aloft Saturday night.

This was the first time the NRO had used a Delta 4-Heavy, which is part of the Air Force's Evolved Expendable Launch Vehicle program that was built to replace the now-returned Titan 4 rocket.

Two more Heavy missions have been purchased by the Air Force from rocket-maker United Launch Alliance. The NROL-32 launch from Cape Canaveral and the NROL-49 flight from California's Vandenberg Air Force Base will carry payloads for the NRO in the next few years.

The next launch for the Delta 4 will use a Medium+ rocket with two strap-on solid motors to haul the GOES-O civilian weather satellite into space. That flight is targeted for the end of April from Cape Canaveral.

0400 GMT (11:00 p.m. EST Sat.)
The initial portion of tonight's launch of the United Launch Alliance Delta 4-Heavy rocket carrying a payload for the National Reconnaissance Office has been called a success.

"This first Delta 4-Heavy launch for the NRO is the culmination of years of hard work and dedication by the combined NRO, Air Force, supplier and ULA team," said Jim Sponnick, ULA Vice President, Delta Product Line.

"We appreciate the support from our mission partners in achieving this milestone. ULA is pleased to contribute to our nation's security, and to continue our strong partnership with the NRO. We look forward to launching many more NRO missions on ULA's Delta 4-Medium, Delta 4-Heavy and Atlas 5 vehicles."

0256 GMT (9:56 p.m. EST Sat.)
The Delta 4-Heavy rocket has flown into a news blackout. The veil of secrecy surrounding the launch of this classified satellite means no further information about the progress of the upper stage engine firings and release of the payload will be announced in real-time. The ultimate outcome of the launch will remain a mystery, as far as the public is concerned.

0254 GMT (9:54 p.m. EST Sat.)
T+plus 7 minutes, 40 seconds. The 65-foot-long, tri-sector nose cone that has enclosed the classified National Reconnaissance Office satellite during ascent through the atmosphere was just jettisoned.

0251 GMT (9:51 p.m. EST Sat.)
T+plus 4 minutes, 45 seconds. The center Common Booster Core's RS-68 engine has revved up to full throttle for the Delta 4-Heavy rocket's on-going journey to space. The booster is identical to the outer strap-on stages, carrying the same propellant supply and engine package, but it employed a more conservative fuel consumption strategy over the past three minutes. That has left enough cryogenic fuel to fire nearly 90 seconds longer.

0250 GMT (9:50 p.m. EST Sat.)
T+plus 3 minutes, 35 seconds. Coming up in about 20 seconds, the outer Common Booster Cores will throttle down as a precursor to engine shutdown and jettison of the stages. It will take five seconds to ease the power setting to 57 percent. The boosters will operate at that throttle for another five seconds before the RS-68s are shut down.

0250 GMT (9:50 p.m. EST Sat.)
T+plus 3 minutes. The Delta 4-Heavy now weighs half of what it did at liftoff. The rocket is burning vast amounts of cryogenic propellant to accelerate away from the planet.

The center engine remains at 57 percent thrust while the starboard Common Booster Core's engines are firing at 102 percent. The outer boosters have just over one minute remaining in powered flight.

0249 GMT (9:49 p.m. EST Sat.)
T+plus 2 minutes. The 8-foot diameter bell-shaped nozzles on the three main engines gimbal during flight, allowing the rocket to steer itself on the intended trajectory eastward across the Atlantic Ocean and toward space.

0248 GMT (9:48 p.m. EST Sat.)
T+plus 1 minute, 45 seconds. The outer Common Booster Cores and their RS-68 main engines continue to consume the supply of super-cold liquid hydrogen and liquid oxygen rocket fuel while firing at full throttle. The RS-68 is considered the world's largest hydrogen-fueled rocket engine. Each powerplant is capable of generating 17 million horsepower.

0248 GMT (9:48 p.m. EST Sat.)
T+plus 1 minute, 30 seconds. The vehicle is ascending through the flight regime that provides the maximum aerodynamic pressures on the rocket. This period is called Max-Q. And the Delta 4-Heavy is breaking the sound barrier as its speed reaches Mach 1.

0247 GMT (9:47 p.m. EST Sat.)
T+plus 55 seconds. The center Common Booster Core's main engine is throttling back to 57 percent thrust as a fuel conservation effort. The starboard and port boosters continue to operate at their maximum power setting of 102 percent thrust.

0247 GMT (9:47 p.m. EST Sat.)
T+plus 30 seconds. All three Pratt & Whitney Rocketdyne RS-68 main engines are firing at full throttle, gulping three tons of propellant per second to produce 1.9 million pounds of thrust.

0246 GMT (9:46 p.m. EST Sat.)
T-minus 30 seconds. The terminal countdown sequencer will take control at T-minus 8.5 seconds. Ignition of the three RS-68 powerplants will follow at T-minus 5.5 seconds. The engines power up to the 102 percent level of thrust for a computer-controlled checkout before liftoff.

0244 GMT (9:44 p.m. EST Sat.)
T-minus 2 minute, 30 seconds. The liquid oxygen tanks in the three Common Booster Cores are confirmed at the proper levels and pressures for flight.

0244 GMT (9:44 p.m. EST Sat.)
T-minus 3 minutes and counting. Replenishment of liquid hydrogen and liquid oxygen to the three Common Booster Cores is being secured in preparation to pressurize the tanks for launch.

0243 GMT (9:43 p.m. EST Sat.)
T-minus 4 minutes, 30 seconds. The systems of the Common Booster Cores and upper stage of the Delta 4-Heavy rocket are switching from ground-fed power to internal batteries.

0242 GMT (9:42 p.m. EST Sat.)
T-minus 5 minutes and counting! Clocks are running again for launch of Delta 4-Heavy rocket on the NROL-26 classified satellite-deployment mission for the National Reconnaissance Office. Liftoff is set to occur at 9:47 p.m. EST (0247 GMT) from pad 37B at Cape Canaveral Air Force Station, Florida.

0241 GMT (9:41 p.m. EST Sat.)
The launch director has instructed the team to pick the countdown for liftoff at 9:47 p.m. EST.

0240 GMT (9:40 p.m. EST Sat.)
The mission director has given his "go" to proceed.

0237 GMT (9:37 p.m. EST Sat.)
The launch team has been polled one more time in preparation for restarting the countdown.

0208 GMT (9:08 p.m. EST Sat.)
T-minus 4 minutes, 30 seconds. The systems of the Common Booster Cores and upper stage of the Delta 4-Heavy rocket are switching from ground-fed power to internal batteries.

0208 GMT (9:08 p.m. EST Sat.)
T-minus 5 minutes and counting! The final phase of today's countdown has commenced for launch of Delta 4-Heavy rocket on the NROL-26 classified satellite-deployment mission for the National Reconnaissance Office. Liftoff is set to occur at 9:13 p.m. EST (0213 GMT) from pad 37B at Cape Canaveral Air Force Station, Florida.

0207 GMT (9:07 p.m. EST Sat.)
And now the launch director has given the final OK to start counting. Liftoff is six minutes away.

0206 GMT (9:06 p.m. EST Sat.)
The mission director representing the government customer for tonight's launch has given permission to continue the countdown.

0205 GMT (9:05 p.m. EST Sat.)
All of the launch team members reported "ready" to restart the countdown.

0204 GMT (9:04 p.m. EST Sat.)
The countdown is holding at T-minus 5 minutes. Another poll of the launch team is being conducted right now to verify all systems are again ready to proceed with the Terminal Countdown. Clocks should resume ticking at 9:08 p.m. for a liftoff of the Delta 4-Heavy rocket at 9:13 p.m. EST (0213 GMT) from Cape Canaveral.

United Launch Alliance says engineers analyzed and now understand what triggered a red alarm that stopped the countdown earlier.

0138 GMT (8:38 p.m. EST Sat.)
There's no estimate of how much longer this delay will last.

0133 GMT (8:33 p.m. EST Sat.)
The launch team reports the Delta 4-Heavy rocket is once again configured for another countdown. However, officials are still working the technical problem that caused the countdown sequencer to stop the earlier launch attempt about one minute before liftoff.

0125 GMT (8:25 p.m. EST Sat.)
The Delta 4-Heavy rocket has been safed and put back into the T-minus 5 minute configuration.

Once this problem is resolved and a new launch time is selected, another countdown will be started from T-minus 5 minutes.

0117 GMT (8:17 p.m. EST Sat.)
United Launch Alliance has not yet said what problem caused the countdown to be stopped. A launch team member called out the hold as the countdown clocks passed T-minus 60 seconds.

0114 GMT (8:14 p.m. EST Sat.)
The launch team is going through the safing procedures following a hold in the final count. The countdown clocks will be reset to T-minus 5 minutes and holding while engineers troubleshoot the problem.

0112 GMT (8:12 p.m. EST Sat.)
HOLD! The countdown has been halted by a problem.

0111 GMT (8:11 p.m. EST Sat.)
T-minus 70 seconds and counting. The Eastern Range has given its "go" for launch.

0111 GMT (8:11 p.m. EST Sat.)
T-minus 90 seconds and counting. All systems are "go" with a minute-and-a-half remaining in the countdown.

0110 GMT (8:10 p.m. EST Sat.)
T-minus 2 minute, 10 seconds. The liquid oxygen tanks in the three Common Booster Cores are confirmed at the proper levels and pressures for flight.

0110 GMT (8:10 p.m. EST Sat.)
T-minus 3 minutes and counting. Replenishment of liquid hydrogen and liquid oxygen to the three Common Booster Cores is being secured in preparation to pressurize the tanks for launch.

0108 GMT (8:08 p.m. EST Sat.)
T-minus 4 minutes, 30 seconds. The systems of the Common Booster Cores and upper stage of the Delta 4-Heavy rocket are switching from ground-fed power to internal batteries.

0108 GMT (8:08 p.m. EST Sat.)
T-minus 5 minutes and counting! The final phase of today's countdown has commenced for launch of Delta 4-Heavy rocket on the NROL-26 classified satellite-deployment mission for the National Reconnaissance Office. Liftoff is set to occur at 8:13 p.m. EST (0113 GMT) from pad 37B at Cape Canaveral Air Force Station, Florida.

0107 GMT (8:07 p.m. EST Sat.)
The launch pad swing arm retraction system pins have been pulled. The three arms will be rotated away from the Delta 4 rocket at liftoff. This system apparently was the source of concern and prompted the delay in tonight's launch time.

0107 GMT (8:07 p.m. EST Sat.)
Now six minutes from launch! The launch director has given final approval to resume the countdown as planned.

0104 GMT (8:04 p.m. EST Sat.)
The final pre-flight poll of the launch team confirms all systems are "ready" for liftoff of the Delta 4-Heavy rocket and its classified spacecraft payload this evening. The targeted launch time is 8:13 p.m. EST.

0055 GMT (7:55 p.m. EST Sat.)
The launch team is resuming countdown activities that are scheduled to be accomplished during the T-minus 5 minute hold. The engineers had paused work while a technical problem was dealt with.

0039 GMT (7:39 p.m. EST Sat.)
The countdown continues holding at the T-minus 5 minute mark. Once this technical issue is resolved, the launch team will finish the activities planned during this hold, including the readiness polls. Then the clocks can start ticking again.

This evening's launch window extends nearly four hours.

0024 GMT (7:24 p.m. EST Sat.)
A new launch time has not been established.

0018 GMT (7:18 p.m. EST Sat.)
Engineers are discussing a technical issue. It appears this hold will be extended, delaying liftoff at least a few minutes.

0013 GMT (7:13 p.m. EST Sat.)
T-minus 5 minutes and holding. The countdown has just entered a planned hold point. Clocks will remain here for 15 minutes to give the launch team members a chance to finish any work running behind schedule and mission officials to conduct final readiness checks. Liftoff is still targeted for 7:33 p.m. EST.

2342 GMT (6:42 p.m. EST)
The three Common Booster Core main engines slew tests are now finished. There were no problems reported in any of the checks, which confirm the rocket will be able to steer itself properly during ascent.

2330 GMT (6:30 p.m. EST)
The team is now preparing to conduct steering checks of the Delta 4 rocket's engines.

2320 GMT (6:20 p.m. EST)
The Range Safety checks have been completed.

2310 GMT (6:10 p.m. EST)
Inhibited checks of the rocket's command destruct receivers are being run. This ensures safety personnel can destroy the Delta 4 rocket if it veers off course or experiences a problem during launch.

2303 GMT (6:03 p.m. EST)
Launch time is 90 minutes away. The rocket has been filled up with fuel for tonight's mission. But as the countdown continues, all eight propellant tanks will be replenished to replace the cryogenics that naturally boil away.

2233 GMT (5:33 p.m. EST)
Just two hours left to go, and it is a beautiful evening on Florida's Space Coast. The clear skies will treat launch watchers to a great view of the three fiery plumes from the Delta 4-Heavy rocket's main engines, as the booster flies eastward away from Cape Canaveral tonight.

2046 GMT (3:46 p.m. EST)
With the CBC liquid hydrogen tanking continuing, the launch team has been given approval to begin chilldown conditioning of the upper stage liquid hydrogen system. This is a precursor to fueling the upper stage.

2040 GMT (3:40 p.m. EST)
The loading of liquid oxygen into the Common Booster Cores has been completed. The launch team will be performing vent and relief checks following tanking and begin chilldown procedures for the upper stage liquid oxygen system.

2033 GMT (3:33 p.m. EST)
Now four hours till launch. The Delta 4 rocket's three Common Booster Cores currently are being loaded with super-cold liquid oxygen and liquid hydrogen propellants.

The cryogenics are fed from the storage tanks through pipelines to the pad. For the three Common Booster Cores, the propellants are routed up to the launch table upon which the rocket sits. Tail service masts, the large box-like structures at the base of the vehicle, feed the oxygen and hydrogen to the boosters via separate umbilicals. The upper stage receives its cryos from the middle swing arm that extends from the Fixed Umbilical Tower to the front-side of the rocket.

2010 GMT (3:10 p.m. EST)
The cold gas chilldown for the hydrogen side has been completed and the launch team is beginning the slow pumping of liquid hydrogen propellant into the three Common Booster Core stages. This "slow-fill" will be sped up to "fast-fill" after a small portion of each tank is loaded.

Chilled to Minus-423 degrees Fahrenheit, the liquid hydrogen will be consumed by the RS-68 main engines along with liquid oxygen during the early minutes of launch.

1955 GMT (2:55 p.m. EST)
As the countdown proceeds toward launch this evening, you can follow along right here on this page.

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1937 GMT (2:37 p.m. EST)
With the Common Booster Cores' liquid oxygen systems properly conditioned for cryogenic temperatures, the loading of Minus-298 degree LOX into the Delta 4-Heavy rocket is about to begin. The liquid oxygen tanks in all three Common Booster Cores will be filled over the next hour or so. The oxidizer will be consumed by the RS-68 main engines during launch.

1929 GMT (2:29 p.m. EST)
The liquid oxygen chilldown is starting in advance of feeding the cryogenic oxidizer into the Delta 4-Heavy rocket this afternoon.

1925 GMT (2:25 p.m. EST)
The "go" has been given for fueling operations. The launch team will start thermal conditioning steps to ready equipment for pumping the super-cold liquid oxygen and liquid hydrogen propellants into the Delta 4-Heavy rocket today. Loading of liquid oxygen into the Common Booster Cores begins first.

1903 GMT (2:03 p.m. EST)
T-minus 5 hours, 15 minutes and counting! The Terminal Countdown has commenced for tonight's launch of the Delta 4-Heavy rocket. With one final hold planned at T-minus 5 minutes, liftoff is still targeted to occur at 7:33 p.m. EST. The available launch window extends about four hours.

The multi-step process of loading all eight cryogenic propellant tanks in the rocket was scheduled to begin in the next half hour and continue into the early evening.

The Delta 4-Heavy is America's largest unmanned rocket currently in service. The giant vehicle is created by taking three Common Booster Cores -- the liquid hydrogen-fueled motor that forms a Delta 4-Medium's first stage -- and strapping them together to form a triple-body rocket, and then adding an upper stage.

The rocket will deploy into space a classified payload for the National Reconnaissance Office. The NRO is the government agency responsible for the country's fleet of spy satellites.

1850 GMT (1:50 p.m. EST)
The launch team has been polled to ensure all stations are manned and systems are ready to proceed with the Terminal Countdown.

1843 GMT (1:43 p.m. EST)
It is time to "man stations for Terminal Count," the launch team was just told.

1803 GMT (1:03 p.m. EST)
T-minus 5 hours, 15 minutes and holding. Clocks have been paused for a planned one-hour hold, during which time the full launch team will be seated at their consoles, the launch pad is scheduled to be cleared of all workers and readiness polls will be conducted by mission management to ensure everyone is ready to proceed with the count.

The Terminal Countdown begins when the clocks resume ticking at 2:03 p.m. EST, leading toward a liftoff of the Delta 4-Heavy rocket at 7:33 p.m. EST from Cape Canaveral.

1750 GMT (12:50 p.m. EST)
We have posted a gallery of pictures taken at pad 37B this morning after rollback of the mobile service gantry. The images can be seen here.

1400 GMT (9:00 a.m. EST)
Preps for a new countdown are underway at frigid Cape Canaveral Air Force Station this morning. Ground crews just completed retracting the pad 37B mobile service tower to reveal the Delta 4-Heavy rocket for tonight's 7:33 p.m. EST launch.

Technicians have fixed the gaseous nitrogen valve problem that delayed the the mission earlier this week. And the odds of good weather for tonight's launch window remain extremely favorable at 90 percent.

"A strong surface area of high pressure is located over Virginia, and
Cape Canaveral is experiencing cold, breezy conditions. Currently winds are from the north gusting to 18 knots at 54 feet and are expected to decrease through the day while becoming northeasterly. With this wind shift brings the possibility of more cold air stratocumulus clouds moving onshore, but this is only a slight concern for launch," meteorologists reported this morning.

The launch forecast calls for scattered clouds at 5,000 and 25,000 feet, 7 miles of visibility, temperature between 55-57 degrees F, northerly winds from 020 degrees at 10 peaking to 16 knots.

The Terminal Countdown will commence at 2:03 p.m. EST today.

FRIDAY, JANUARY 16, 2009
Expecting cooperation from Mother Nature and finally a resolution to this week's trouble with a gaseous nitrogen valve on the pad, the Delta 4-Heavy rocket will shoot for launch Saturday evening.

Liftoff from Cape Canaveral's Complex 37 is targeted for 7:33 p.m. EST, which is the opening of a four-hour launch opportunity.

Earlier plans to launch this rocket and its clandestine satellite cargo on Tuesday were scrapped so workers could make minor repairs to damaged foam insulation on the vehicle's interstage, then the valve problem forced a scrub during Wednesday's countdown. The valve issue continued to be addressed Thursday, and managers decided to skip any launch attempt Friday due the low odds of acceptable weather conditions.

So that sets up a Saturday countdown, when there's a predicted 90 percent chance of good weather and the gaseous nitrogen system, which is necessary to assist in fueling the rocket, should be fixed.

This will be the third flight of the Delta 4-Heavy, the largest unmanned booster used by the U.S. to deploy satellites, following a December 2004 test launch and the first operational mission in November 2007.

From the outside, the rocket looks almost identical to the configuration flown on the last mission. Standing 23 stories tall, the Heavy's triple-wide hydrogen-fueled stages provide 1.9 million pounds of thrust at liftoff. And the upper stage is equipped with a powerful cryogenic engine capable of multiple maneuvers for delivering the payload into its intended orbit. An aluminum nose cone 16 feet in diameter and 65 feet long, a heritage shroud from the now-retired Titan 4 program, will protect the secret cargo during ascent through Earth's atmosphere.

The Air Force says only a few changes have been made to the Heavy since its operational debut 14 months ago.

"One change has been a slight modification to the thermal barrier assembly which was modified to reduce the amount of normal unburned hydrogen gas which could pass through the thermal barrier and into the first stage engine section during the early stages of flight," according to information provided to Spaceflight Now by the Space and Missile Systems Center's Launch & Range Systems Wing.

"This action was taken to mitigate the potential recurrence of the Port Common Booster Core engine section pressure and temperature excursion seen on the DSP 23 launch."

The DSP 23 missile-warning satellite launch and the rocket demonstration flight four years ago have paved the way for Saturday's flight carrying a classified satellite for the U.S. National Reconnaissance Office, a mission officially known as NROL-26.

"The Heavy Demo mission verified the mission profile, and DSP 23 verified the vehicle changes from the Heavy Demo mission," the Air Force said.

The demonstration launch carrying a simulated payload uncovered a problem with vapor bubbles in the liquid oxygen lines that caused the rocket's engines to shut down prematurely and left the mission well short of the targeted altitude. The problem was solved before the DSP 23 launch.

Both previous rockets carried extensive instrumentation and sensors to measure the conditions and environments experienced during launch, plus precisely determine the vehicles' performance. In fact, the 2007 mission relayed over a thousand channels of data from standard and extra instrumentation and the launch was imaged by a network of ground-based and onboard video cameras. Officials said the initial post-flight gathering of engineers to analyze the mission had a couple thousand pages of graphs to review.

Two more Heavy missions have been ordered by the Air Force from rocket-maker United Launch Alliance. The NROL-32 launch from Cape Canaveral and the NROL-49 flight from California's Vandenberg Air Force Base will carry payloads for the National Reconnaissance Office in the next few years. Specific launch dates "have not yet been formalized," the Air Force said.

The Delta 4-Heavy was developed by Boeing as part of the Evolved Expendable Launch Vehicle program that includes various rocket configurations to carry the nation's spacecraft to orbit. The other EELV rocket family -- the Atlas 5 created by Lockheed Martin -- could field a Heavy version too. But the Air Force says there remains no need to build an Atlas 5-Heavy.

"Due to the existing Delta 4 capability and the current manifest, the Air Force does not plan to advance the development of the Atlas 5-Heavy configuration," the Launch & Range Systems Wing said.

THURSDAY, JANUARY 15, 20092340 GMT (6:40 p.m. EST)
Saturday evening will be the next attempt to launch the Delta 4-Heavy rocket on its classified satellite-deployment mission. Liftoff time is scheduled for 7:33 p.m. EST.

The bleak weather forecast for Friday at Cape Canaveral led launch officials to forego taking a shot of counting down tomorrow.

"The forecast for Friday predicts a 70 percent chance of high winds exceeding both Mobile Service Tower roll and launch criteria. The forecast Saturday significantly improves to only a 20 percent chance of weather violating launch criteria," officials announced in a press statement.

The problem with a gaseous nitrogen valve in the launch pad ground support equipment "will be fully repaired and mission capable" to support Saturday's launch, officials said.

2010 GMT (3:10 p.m. EST)
If the launch is rescheduled for Friday evening, meteorologists say the weather could pose a real challenge. The updated weather forecast issued this afternoon says there's just a 30 percent chance of acceptable launch conditions on Friday evening due to high winds and thick clouds.

"A reinforcing cold front will move through the area Thursday evening. Thick layered clouds, increasing ground level winds and colder temperatures can be expected after frontal passage and will continue through Friday," the weather team says.

Northerly winds of 18 peaking to 25 knots are predicted on Friday evening.

But the outlooks for Saturday and Sunday are much better. There's 80 percent and 90 percent chances, respectively, of favorable conditions for the Delta 4-Heavy on those days. Ground winds are expected to be the main concern this weekend.

1830 GMT (1:30 p.m. EST)
Launch officials will hold a meeting later tonight to select a new target launch date. The gaseous nitrogen valve problem continues to be worked and weather is becoming a new factor in the discussions about launch date options.

Information about the new launch date and time will be posted here on this page as soon as the information is announced. And if you will be away from your computer, sign up for our Twitter feed and get text message updates on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)

1732 GMT (12:32 p.m. EST)
SCRUB. Today's launch attempt has been cancelled, officials just announced. Pad crews were instructed to begin preps to move the pad's gantry back into position around the Delta 4-Heavy rocket at Complex 37.

An official new launch date is pending.

1655 GMT (11:55 a.m. EST)
United Launch Alliance and its U.S government customer hope to see the Delta 4-Heavy rocket head out of Cape Canaveral and into space later tonight.

ULA says work to resolve the ground support equipment issue that prompted yesterday's scrub continues to be worked. But early countdown steps are beginning at pad 37B and in the launch control center to support a 7:41 p.m. EST liftoff this evening.

The Terminal Countdown is slated to start at 2:11 p.m. EST.

1435 GMT (9:35 a.m. EST)
The launch weather team continues to predict a 70 percent chance of acceptable conditions for this evening's launch opportunity. And if the launch happens to slip to Friday night, the odds of favorable weather drops to 60 percent. Ground winds will be the concern both nights.

"A reinforcing cold front will move through the area Thursday evening. No precipitation will be associated with this front; however, increasing ground level winds and colder temperatures can be expected after frontal passage," forecasters reported this morning.

"The wind will continue to increase Friday causing a greater concern for a ground wind (Launch Commit Criteria) violation for the 24-hour delay forecast."

Tonight's outlook includes a few clouds at 25,000 feet, 7 miles of visibility, northerly winds from 340 degrees at 12 peaking to 18 knots and a temperature between 52-54 degrees F.

WEDNESDAY, JANUARY 14, 2008
To recap, tonight's launch was scrubbed by a ground equipment issue that had pushed countdown activities well behind schedule. The launch team will prepare for another countdown on Thursday, leading toward a 7:41 p.m. EST liftoff time from Cape Canaveral, Florida.

The scrub was called to the launch team at 6:09 p.m. EST, a few hours after fueling of the rocket with liquid hydrogen and liquid oxygen propellants was supposed to have started. A gaseous nitrogen relief valve problem at pad 37B held up the timeline of events during the afternoon.

"The very dry gaseous nitrogen is used to evacuate the air from various compartments in the launch vehicle whenever cryogenic propellants are loaded, because the extremely cold temperatures of the propellants would cause water in the air to condense," United Launch Alliance said in the post-scrub press release. "Without this piece of equipment working properly fueling of the vehicle could not take place and the issue could not be resolved in time to make tonight's launch window."

2323 GMT (6:23 p.m. EST)
Tomorrow's launch time is targeted for 7:41 p.m. EST. The window will last about four hours.

Meteorologists are calling for a few clouds at 25,000 feet, 10 miles of visibility, northerly winds from 350 degrees at 12 peaking to 18 knots and a temperature between 52-54 degrees F.

2309 GMT (6:09 p.m. EST)
SCRUB. Tonight's launch of the Delta 4-Heavy rocket from Cape Canaveral Air Force Station in Florida has been called off. That decision was announced to the launch team a few seconds ago.

A gaseous nitrogen valve problem being addressed at launch pad 37B prevented the team from proceeding into most of the countdown activities, including the multi-hour job of fueling the rocket.

Officials said the launch would be tentatively rescheduled for Thursday evening, giving technicians time to resolve the ground equipment issue before starting a fresh countdown.

2250 GMT (5:50 p.m. EST)
The local weather remains ideal for a launch tonight. Skies are crystal clear and ground winds are light.

2225 GMT (5:25 p.m. EST)
The launch team just completed radio frequency link checks to verify good telemetry streams between the rocket and the receiving station at the Cape.

2210 GMT (5:10 p.m. EST)
Work continues to resolve the problem with a gaseous nitrogen relief valve in ground support equipment at launch pad 37B. Once technicians successfully fix the issue, fueling of the Delta 4-Heavy will commence and officials will be able to assess when the rocket can launch tonight.

2150 GMT (4:50 p.m. EST)
Clocks continue to count toward this evening's launch window that opens at 7:45 p.m. EST and extends about four hours. The loading of supercold liquid hydrogen and liquid oxygen into the rocket has not yet started. How this delay will impact tonight's target liftoff time remains to be seen. We'll pass along further information as it becomes available.

2045 GMT (3:45 p.m. EST)
Launch preparations remain in a holding pattern right now. The team has been dealing with a gaseous nitrogen problem that has prevented fueling from getting underway as originally scheduled today.

1950 GMT (2:50 p.m. EST)
Our gallery of images taken this morning showing the mobile service tower rolling back to reveal the Delta 4-Heavy rocket is posted here.

1935 GMT (2:35 p.m. EST)
Technicians are working to clear up a gaseous nitrogen valve issue at launch pad 37B. Officials estimate another 30 minutes to finish that work, than an hour to clear the pad before fueling operations can begin.

Countdown clocks will continue to tick this afternoon and the launch team will get started with fueling operations as soon as possible.

1915 GMT (2:15 p.m. EST)
T-minus 5 hours, 15 minutes and counting! The Terminal Countdown has commenced for this evening's launch of the Delta 4-Heavy rocket and a top-secret payload for the U.S. National Reconnaissance Office. With one planned hold at T-minus 5 minutes, liftoff is still targeted for 7:45 p.m. EST. The available launch window extends about four hours.

Once all workers are clear of the launch pad, which has not yet occurred, the multi-step process of loading all eight cryogenic propellant tanks in the rocket will begin.

1901 GMT (2:01 p.m. EST)
Launch team members have been polled to ensure everyone is ready to begin Terminal Count at the end of this built-in hold.

1830 GMT (1:30 p.m. EST)
The call to "man stations for Terminal Count" just went out to the launch team.

1815 GMT (1:15 p.m. EST)
T-minus 5 hours, 15 minutes and holding. Countdown clocks are entering a planned one-hour hold in today's launch operation at Cape Canaveral's Complex 37. During this hold, the full launch team will be seated at their consoles, the launch pad will be cleared of workers and readiness polls will be conducted by mission management to ensure everyone is ready to proceed with the count.

The Terminal Countdown begins when the clocks resume ticking at 2:15 p.m. EST.

1550 GMT (10:50 a.m. EST)
The mobile service tower has been moved away from the Delta 4-Heavy rocket, allowing workers to proceed onward with today's checklist of chores needed to configure and secure the pad for the countdown.

Rollback began at 10 a.m. and the tower was clear of the rocket about 10 minutes later. It took the gantry about 30 minutes to reach its parking spot for launch.

The Terminal Count is scheduled to begin at 2:15 p.m. EST, some five-and-a-half hours before the targeted liftoff time. The countdown will be spent fueling the eight cryogenic fuel tanks aboard the rocket, testing critical systems and verifying the hardware is ready to fly.

At 7:25 p.m., the countdown enters a planned 15-minute hold at the T-minus 5 minute mark. This offers managers a chance to perform final readiness polls of the entire launch team to confirm there are no issues or concerns before entering the last phase of the countdown.
Assuming all systems are go, clocks will resume ticking at 7:40 p.m. During those final five minutes, the rocket will switch to internal power, ordnance will be armed, all eight propellant tanks will be secured and the Range will announce a clear-to-launch.

At T-minus 14 seconds, the sparkler-like radial outward firing ignitors -- or ROFIs -- are started beneath the main engine nozzles. The Terminal Countdown Sequencer will grab control at T-minus 8.5 seconds to manage events in the crucial last seconds and oversee the rocket's status. The ignition sequence for the three RS-68 powerplants follows at T-minus 5.5 seconds as the main hydrogen fuel valve in each engine is opened. As fuel floods through the engines, spectacular flame erupts at the base of the rocket as free hydrogen reaches the ROFIs.

The oxygen valves in the engines are opened at T-minus 2 seconds as the RS-68s begin roaring to life. The engines must rev up to full throttle -- 102 percent thrust level -- and undergo a rapid computer-controlled health check to ensure all parameters are met.

If any problem is detected before T-minus 40 milliseconds, the engines will shut down and the rocket prevented from lifting off.

A successful engine startup leads to T-0 as the 12 hold-down bolts that have been restraining the rocket to Earth finally detonate. The 23-story, 1.6-million pound vehicle blasts off at 7:45 p.m. EST (0045 GMT) on the NROL-26 classified satellite-deployment mission.

Each booster core features a Pratt & Whitney Rocketdyne RS-68 main engine that generates 650,000 pounds of thrust while burning supercold liquid hydrogen and liquid oxygen.

About 50 seconds into flight, the center Common Booster Core's engine is throttled back to its minimum power level of 57 percent thrust to conserve fuel that becomes important later. The starboard and port boosters continue firing at full throttle -- 102 percent thrust -- through the launch's first four minutes before emptying their liquid hydrogen and liquid oxygen propellant tanks and shutting down the RS-68 engines. The 15-story boosters will peel away and plummet into the Atlantic Ocean.

Once the outer boosters are shed, the center stage finally throttles back up to 102 percent for more than a minute of propulsion, consuming that fuel supply saved during the period of reduced thrust. Once the stage is jettisoned, the rocket's cryogenic upper stage powered by a Pratt & Whitney Rocketdyne RL10B-2 engine will continue the push to orbit.

The 65-foot-long shiny white metallic nose cone, originally developed to shroud payloads on Titan 4 rockets, is jettisoned after the upper stage is ignited.

Soon thereafter, the launch will enter a news blackout and no further information about the secretive mission is expected.

Retraction of the 330-foot tall mobile service tower from around the rocket is expected to begin a little later this morning. The wheeled gantry structure moves along rail tracks to its launch position about the length of a football field from the rocket's mount.

The 9-million pound tower shields the Delta 4 from the weather, provides workers 360-degree access to the various areas on the vehicle and is needed to hoist the payload atop the upper stage during the launch campaign. The tower is 90 feet wide and 40 feet deep.

The Cape's Complex 37 is the same site used in the 1960s to fly unmanned Saturn 1 and 1B rockets that helped prepare for mankind's voyage to the moon. The site was rebuilt for the Delta 4 era, successfully supporting six liftoffs in the next-generation vehicle family so far.

The weather forecast for tonight's launch opportunity remains excellent. There's just a five percent chance of ground winds being a problem.

"A cold front moved through last night and the associated clouds and
weather are currently moving through South Florida. High pressure will build in from the west, bringing favorable weather for launch. There is only a slight concern for a violation of the ground wind (54 ft) Launch Commit Criteria (LCC)," the Air Force weather team reported this morning.

The forecast calls for scattered cirrus clouds at 25,000 feet, 7 miles of visibility, a temperature between 52-53 degrees F and northerly winds from 010 degrees at 8 peaking to 14 knots.

WEDNESDAY, JANUARY 14, 2009
It is launch day at Cape Canaveral Air Force Station for the Delta 4-Heavy rocket carrying a clandestine reconnaissance satellite for the U.S. intelligence community. Liftoff of America's largest unmanned rocket is scheduled for 7:45 p.m. EST this evening.

Watch this page for live updates throughout the countdown.

TUESDAY, JANUARY 13, 2009
The classified launch of the Delta 4-Heavy rocket has been rescheduled for 7:45 p.m. EST on Wednesday evening.

Today's launch opportunity was called off about 12 hours before liftoff time to repair damaged insulation on the rocket.

"During final walk down inspections, some minor damage to the spray-on
foam insulation for the interstage doors was discovered. This
insulation will be repaired prior to flight, but the work will not be
completed in time to support the roll of the mobile service tower as
planned for today," the Air Force said.

1605 GMT (11:05 a.m. EST)
Air Force meteorologists are predicting ideal weather conditions for a Wednesday liftoff of the Delta 4-Heavy rocket from Cape Canaveral, Florida. There is a 90 percent chance of acceptable conditions, with ground-level winds posing only a slight concern.

"The front that stalled to the south of Cape Canaveral yesterday returned
back over the area as a warm front this morning. An upper level trough will enter the Southeast U.S. this evening, pushing the surface front though Central Florida again as a cold front," the latest forecast says.

"The front will cause thick layered clouds, precipitation, and windy conditions early this evening. This weather will clear overnight, and high pressure will build in from the west, bringing favorable weather for launch Wednesday evening. There is only a slight concern for a violation of the ground wind (54 ft) Launch Commit Criteria."

The forecast calls for scattered cirrus clouds at 25,000 feet, 7 miles of visibility, a temperature between 52-53 degrees F and northerly winds from 010 degrees at 8 peaking to 14 knots.

1255 GMT (7:55 a.m. EST)
SCRUB. This evening's launch of the Delta 4-Heavy rocket carrying a classified payload for the U.S. National Reconnaissance Office has been postponed by 24 hours.

The available launch window will last about four hours, giving an extensive amount of time to work any technical problems or wait out the weather and still have a chance of getting the rocket off the ground Tuesday night.

"Cold frontal boundary which passed through the area this morning will stall over the southern half of Florida. In addition, a strong upper level disturbance moving across the southeast U.S. will induce low pressure along the stalled front, resulting in the front returning northward as a warm front. Low pressure will move quickly across Florida tomorrow evening which will again cause the front to move south as a cold front. Thick layered clouds and precipitation and windy conditions will be a concern until the entire system moves through late tomorrow night and into Wednesday. There remains model inconsistency so further changes can be expected," the official weather forecast says.

The forecast calls for broken decks of clouds at 5,000 and 10,000 feet, overcast conditions at 20,000 feet, 7 miles of visibility, a temperature between 60-62 degrees F and northwesterly winds from 300 degrees at 15 peaking to 22 knots.

If the launch is postponed for some reason, the odds of acceptable weather are much better on Wednesday evening. There's just a 10 percent chance of high winds being a problem on the backup launch date.

SUNDAY, JANUARY 11, 2009
America's heavy-lift rocket, the towering white and orange triple-barreled booster responsible for launching vital security and intelligence satellites, will make another of its spectacular ascents Tuesday evening from Cape Canaveral.

Liftoff of the United Launch Alliance Delta 4-Heavy rocket is scheduled to occur sometime between 7 p.m. and midnight EST, but the exact timing won't be revealed until Monday afternoon.

In fact, most of the details surrounding the launch will never be publicly announced because of the classified satellite payload riding atop the 23-story rocket.

The U.S. National Reconnaissance Office, the secretive government agency that designs and operates the country's spy satellites, is using the Delta 4-Heavy to send a large spacecraft into orbit. The NRO doesn't disclose the identities of the satellites it is launching or what the craft will do.

Officials say a news blackout will begin about 8 minutes after liftoff, soon after the rocket's upper stage ignites and the aluminum nose cone shrouding the payload is jettisoned. The rest of the hush-hush flight is expected to remain a mystery, as far as the public is concerned.

"The flow of official information about this mission will cease at the point of payload fairing separation. No further comment about the status of the mission will be made after this milestone," the Air Force's pre-launch news media advisory said.

The Delta 4-Heavy rocket was rolled to launch pad 37B in late March to start the pre-flight campaign of readying the mammoth booster. Its sophisticated cargo was brought out to the seaside pad a few months later.

Technicians and engineers have spent a long time preparing for this undoubtedly high-dollar launch. It was one of the missions included in the original batch of launches awarded to the Delta 4 a decade ago. Now, all appears set to go Tuesday evening.

The mobile service gantry will move away from the rocket by mid-morning, clearing the way for the countdown to commence. The multi-hour fueling operations will run from early afternoon until after the sun goes down.

The Heavy will be making its third flight following a demonstration test launch conducted in December 2004 and the first operational mission in November 2007 that orbited a missile-warning satellite for the U.S. military.

"Both of those were very momentous launches. There were some very senior Air Force and Defense Department folks who characterized Heavy Demo as the most challenging U.S. space launch since the first shuttle flight. It's a fully cryogenic vehicle, three different bodies. It was definitely a major accomplishment to get through that demo flight," the Air Force's former Delta commander said in previous interview.

The test flight, which carried a simulated payload, uncovered an unexpected problem with vapor bubbles in the booster cores' liquid oxygen fuel lines that caused all three main engines to shut down a few seconds early and resulted in the final orbit falling short of the target. Hardware and computer software changes were implemented to prevent a reoccurrence on future launches.

The fixes worked and the Heavy achieved a "spot-on" orbital delivery of its first real payload during the 2007 operational debut.

The Heavy is the biggest booster in the Air Force's Evolved Expendable Launch Vehicle family of rockets. It is capable of carrying the military's largest and heaviest payloads that once relied upon the now-retired Titan rocket fleet.

"I really don't think you can say the EELV program has come of age until you can demonstrate a milestone of launching an operational Heavy," the commander said.

The Heavy vehicle is created by taking three Common Booster Cores -- the liquid hydrogen-fueled motor that forms a Delta 4-Medium's first stage -- and strapping them together to form a triple-body rocket, and then adding an upper stage.

"Heavy is kind of the centerpiece of the family, and being able to get through that (operational debut) really was rewarding. I think it was important to the nation and demonstrated our capability to stay on the performance spectrum of what we need to launch our national security satellites. It was a huge deal."

Both previous Heavy launches saw the upper stage perform three firings in missions that targeted circular orbits at geosynchronous altitude 22,300 miles above the planet. The Air Force has said in the past that Tuesday's launch, which is known as the NROL-26 mission, will be another three-burn ascent profile that follows a launch timeline similar to the one demonstrated during the 2004 test flight. That would mean the upper stage performs its first two maneuvers in quick succession, then takes a long orbital coast before delivering a final boost and releasing the payload to complete the launch.

The launch is being dedicated to the memories of the NRO's Dennis Fitzgerald and ULA's Ken Liptak.

Fitzgerald worked in the intelligence community for 33 years and served as the agency's principal deputy director at the time of his retirement in 2007. He continued to support the organization he loved until his death on December 31, 2008.

"Dennis Fitzgerald was a superb engineer, manager, leader, mentor and friend. He was a role model for all of us in his passionate dedication to engineering and acquisition excellence, and the protection of our national security," the NRO's director recently wrote. "His legacy lives on in the systems he put on orbit and the service he inspired in the NRO workforce."

Liptak began his career with McDonnell Douglas in the early 1990s as a contract manager for the Delta 2 program and spent most of his career at the launch sites. After ULA was formed in 2006, he was the business team leader for the launch sites on both coasts.

"Ken's dedication and innovative approach leave a legacy at ULA that will be felt for years to come and his style, his smile, his wit and his genuine caring will be missed by all who worked with him," the ULA dedication reads.

FRIDAY, JANUARY 9, 2009
The early weather projections for Tuesday night's launch of the Delta 4-Heavy rocket carrying a classified reconnaissance satellite calls for breezy and chilly conditions at Cape Canaveral Air Force Station.

Meteorologists issued their initial forecast this morning and put the odds of acceptable launch weather at 70 percent. Gusty winds at pad 37B will be the main concern.

A mostly dry weather front is predicted pass through the Central Florida region on Tuesday, bringing increased ground winds in its wake.

The forecast calls for a few low clouds at 5,000 feet and a few high clouds at 20,000 feet, 10 miles of visibility, a temperature between 50-52 degrees F and westerly winds from 290 degrees at 12 peaking to 18 knots.

Based on that wind direction, the launch limit is 20 knots.

It will be the first rocket flight of 2009 from Cape Canaveral or any other global launch site. Liftoff is anticipated sometime between 7 p.m. and midnight EST. The exact launch time won't be revealed until Monday afternoon as part of the security restrictions surrounding this military mission.

The Delta 4-Heavy is America's largest unmanned rocket currently in service. The giant vehicle is created by taking three Common Booster Cores -- the liquid hydrogen-fueled motor that forms a Delta 4-Medium's first stage -- and strapping them together to form a triple-body rocket, and then adding an upper stage.

The rocket will deploy into space a top-secret payload for the National Reconnaissance Office. The NRO is the government agency responsible for the country's fleet of spy satellites.

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